X-ray binaries consist of a massive compact object, either a neutron star or a black hole, and a close companion star, usually on the main branch. If too close, the companion star overflows its Roche lobe and material streams towards the compact object, forming a small accretion disk. The disk emits radiation primarily in X-rays, but over time this radiation exhibits a rich set of variations that is telling us important information about the system. In particular, X-ray binaries support a set of well-defined quasi-periodic oscillations (QPOs), some of which are probably connected to large-scale disk oscillations and/or disk features, which in turn depend on general relativistic effects. As a consequence, QPOs provide a means to probe strong gravity.

I am beginning to be interested in the various global waves and instabilities that such disks can support and how they connect to warps and eccentricities. The main application is to QPOs in X-ray binaries, but AGN, dwarf novae, and protoplanetary disks are also venues in which this physics crops up. The three main thrusts of my work presently are (a) the role of magnetic fields and how they may inhibit or destroy waves and oscillations, (b) how an imposed eccentricity excites standing waves in the inner parts of relativistic disks, and (c) how magnerotational turbulence interferes with these oscillations. Another related project aims to explain the provenance of oscillations in Be disks, which are disks formed from material expelled from a B star.

Potential PhD topics include
*The impact of MRI turbulence on eccentricity-fueled inertial oscillations
*The impact of MRI turbulence on the Papaloizou-Pringle instability (see figure below)
*The viability of the accretion-ejection mechanism
*The role of the disk-star boundary layer in Be disk oscillations

Recent papers:

*Quasi-periodic oscillations, trapped inertial waves and strong toroidal magnetic fields in relativistic accretion discs (link)
*Quasi-periodic oscillations and the global modes of relativistic, MHD accretion discs (link)